Abstract: The amidosulfonates of Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ were prepared by the direct reaction between the metal carbonate and the amidosulfonic acid with heating and stirring. The compounds were characterized by infrared absorption spectroscopy (IRFT), elemental analysis, thermal analysis (TG and DTA) and X-ray diffraction by the powder method. The absorptions observed in IR spectra are associated with N-H and O-H stretching, as well as symmetrical and asymmetric S-O stretching in the sulfonic group. The compounds present X-ray diffraction pattern with well-defined reflections, showing no evidence of isomorphism. The TG-DTA curves allowed to establish the stoichiometry of compounds as M(NH2SO3)2.xH2O, where M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ and x ranging from 1 to 4. Dehydration leads to the formation of stable anhydrous. In all cases the respective sulfates are formed as an intermediate. After consecutive steps of decomposition, the respective oxides were obtained: Mn3O4, CoO, NiO, CuO and ZnO. The TG-DTA curves are characteristic for each sample, with thermal events related to dehydration and ligand decomposition.
Keywords:sulfamic acidsulfamic acid,thermal behaviorthermal behavior,sulfamatessulfamates,transition metalstransition metals.
Synthesis, characterization, and thermal behavior of amidosulfonates of transition metals in air and nitrogen atmosphere
Universidade Estadual Paulista Júlio de Mesquita Filho
Received: 29 January 2020
Accepted: 11 May 2020
Published: 01 October 2020
The amidosulfonic acid or sulfamic acid (NH2SO3H) has molar mass 97.10 g mol-1. When dry it is stable, but in solution, it is easily hydrolyzed, forming ammonium bisulfate. It is relatively soluble in water, moderately soluble in alcohol, poorly soluble in acetone, insoluble in ether and very soluble in nitrogenous bases, liquid ammonia, pyridine, formamide and dimethylformamide. It is classified as a strong acid (pH = 1.2 in 1% aqueous solution and 25 oC). It is used as standard in alkalimetry, in steel cleaning, in removal of nitrites and stabilization of chlorine in pool water. It is a toxic compound, used as poison for rats. Handling requires careful care as it easily irritates the skin and mucous membrane. It forms orthorhombic crystals and has melting point near 205 oC1. In recent years sulfamic acid has been used as an efficient heterogeneous catalyst in a series of organic reactions, such as acetylation, esterification, condensation, transesterification, among others2. It is a ZWITTERION, in other words, a dipolar ion having opposite charges on different atoms. In the formation of metal complexes, both amine and sulfonate groups participate in the coordination with the metal ion.
Few studies report the chemical and thermal properties of metal salts containing sulfonic acid derivatives, although the preparation of these salts is easy to perform3-10. Maksin and Standritchuk3 studied the water solubility of Ni(II) and Co(II) sulfamates. Budurov et al.4,5 studied by DSC the phase transformations that occur in the heating of some amidosulfonates, determining the energy involved in the processes represented by endothermic peaks. Also, by DSC, Thege6 investigated the thermal behavior of (NH4)2SO4, NH4HSO4 and NH4NH2SO3. The crystalline structure and growth of Li[NH2SO3] monocrystals was studied by Stade, Held and Bohaty7, and it was possible to establish the spatial group, cell parameters and refractive index for the crystals obtained. The elastic properties of sulfamic acid and various sulfamates were studied by Haussül and Haussül and reported phase transformations8. Shimizau et al.9 determined the crystallographic properties of silver amidosulfonate and described a lamellar structure with potential chemical applications. Squattrito and coworkers studied the layered structures of metal salts of sulfonic acid derivatives10-12. Jaishree et al.13 studied the optical and thermal properties of a monocrystal of amidosulfonic acid and reported the absorption bands in the infrared region. The main absorptions were attributed to the vibrational modes of the -SO3- and -NH3+ group. Brahmaji et al. also identified the functional groups by FTIR and reported the changes observed in the pure crystals and doped with Tb3+ 14. Wickleder15 studied the synthesis, crystal structure, and thermal behavior of some rare earth amidosulfonates. Luiz, Nunes and Matos16 studied the thermal behavior of all the amidosulfonates of the rare earth series and observed a mass gain between 250 oC and 350 oC, attributed to an oxidative process SO32- → SO42-, which is more evident in a lower heating rate. Brahmaji et al.14 also observed mass gain in this temperature range.
All chemicals used in this study were of analytical grade. Metallic chlorides were obtained from Sigma Aldrich, while the sodium hydrogen carbonate and silver nitrate were obtained from Merck and were used without further purification.
Carbonates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) were prepared by adding slowly, with continuous stirring, a saturated sodium hydrogen carbonate solution to aqueous solutions metal chloride, until total precipitation of the metal ions. The precipitates were washed with distilled water until the elimination of chloride ions (qualitative test with AgNO3/HNO3 solution for chloride) and was placed in vacuum desiccator until constant mass.
The compounds were prepared by the direct reaction between the aqueous suspension of the metal carbonates (Mn, Co, Ni, Cu and Zn) and the amidosulfonic acid, with heating at 80 oC and stirring. The acid in powder form was slowly added until a small amount of the metal carbonate remained. The carbonate in excess was removed by filtration and the aqueous solution was evaporated slowly near to dryness. Subsequently, the solution was kept in vacuum desiccator until constant mass.
The infrared spectroscopy for amidosulfonic acid and its metal amidosulfonates were run on a Perkin-Elmer Spectrum 100 ATR FTIR spectrophotometer using ATR accessory with germanium crystal. The FTIR spectra were recorded with 16 scans per spectrum a resolution of 4 cm-1.
The X-ray powder patterns were obtained by using a BRUKER System D8 Advance Diffractometer, employing CuKα radiation (λ = 1.541 Å), 25 mA, 40 kV, 10 rpm rotation, 0.02 step, 0.6 slit mm, time 0.3 s, in the range 20 from 10 to 70 degrees. Elemental analysis for H, N and S was performed using a Leco CHNS Analyzer.
The thermal behavior was evaluated by thermogravimetry (TG) and differential thermal analysis (DTA) in the simultaneous module TG-DTA 6200 Extar 6000 from Seiko SII, with sample mass of the order of 3 to 10 mg, heating ratio ß = 20 oC min-1 (30 to 900 oC), alumina crucible, dynamic atmosphere of synthetic air and nitrogen, with flow of 100 mL min-1. As reference for DTA, previously calcined alumina was used.
The elemental analysis results are presented in Tab. 1 and are in agreement with the proposed general formula M(NH2SO3)2.xH2O, where M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ and x the number of water molecules ranging from 1 to 4, where x = 4 for Mn2+, 3 for Co2+ and Zn2+, 2 for Ni2+ and 1 for Cu2+.
Elemental analysis of the solid compounds.
The main infrared absorption bands were associated with the N-H stretching, namely, a NH3+ broad band at 3400-3300 cm-1, the N-H stretching as a weak band at 2873 cm-1 and the absorptions observed at 1533 and 1433 cm-1 due to symmetric stretching mode of NH3+ while at 1567 cm-1 is due to asymmetric mode. The SO3- stretching vibration was observed in a 1065 cm-1 and at 685 cm-1, the N-S stretching mode can be seen, all these absorptions agree with the literature4-14. The absence of that weak band of N-H stretching is an evidence that de coordination of the metal ions occurred by NH3+ group. Another fact is the increase observed in the wavenumber for the N-S stretching, suggesting that the N-S bond becomes strongest. The vibrational spectra in the infrared region of amidosulfonic acid and metal amidosulfonates are show in the Fig. 1.
The X-ray powder pattern of the metal amidosulfonates are shown in the Fig. 2. The X-ray diffractograms indicate that the compounds were obtained with a certain crystallinity degree, showing no evidence of isomorphism. The compounds showed low relative intensity (Io) reflections: Mn (2θ = 19.0; Io; = 845); Co (2θ = 19.3; Io = 3621); Ni (2θ = 26.3; Io = 6534); Cu (2θ = 25.4; Io = 4010); Zn (2θ = 19.4; Io = 4146).
By the TG/DTA curves it was possible to establish the stoichiometry of the compounds, such as: ML2.xH2O, where M represents the metallic ions M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+; L represents the anion NH2SO3- and x the number of water molecules ranging from 1 to 4, where x = 4 for Mn2+, 3 for Co2+ and Zn2+, 2 for Ni2+ and 1 for Cu2+. In a synthetic air atmosphere, the events associated with the thermal decomposition of the ligand occur at slightly lower temperatures than in a nitrogen atmosphere. Tables 2 and 3 show the results extracted from the TG and DTA curves in the atmosphere of synthetic air and nitrogen. Figures 3 and 4 show the TG and DTA curves in the atmosphere of synthetic air and nitrogen, respectively.
Figure 1.
Vibrational spectra in the infrared region of amidosulfonic acid and metal amidosulfonates.
Figure 2.
X-ray diffraction pattern of the metal amidosulfonates.
Figure 3.
TG and DTA curves of the obtained compounds, in a synthetic air atmosphere. Sample mass: Mn = 9.680 mg, Co = 2.980 mg, Ni = 10.194 mg, Cu = 10.314 mg and Zn = 10.064 mg.
Figure 4.
TG and DTA curves of the obtained compounds, in a nitrogen atmosphere. Sample mass: Mn = 10.383 mg, Co = 3,794 mg, Ni = 2,984 mg, Cu = 10.414 mg and Zn = 10.193 mg.
Results extracted from the TG curves.
Results extracted from the DTA curves.
Dehydration of the manganese (II) amidosulfonate occurs in two consecutive steps with the elimination of one and subsequently three water molecules, between 30 and 220 °C, with mass loss about 22 %. In this step two endothermic peaks are observed at 90 oC and 148 oC (synthetic air) at 85 oC and 147 oC (N2). The anhydrous compound remains stable between 219 oC and 340 oC (synthetic air) and between 197 oC and 333 oC (N2). Although no mass change was observed in this temperature range, there is an exothermic peak at 289 oC (synthetic air and N2) which may be associated with a crystallization process. Brahmaji et al.14 also reported a gain mass in this range temperature, however this thermal event needs to be further investigated. Budurov et al.5 reported endothermic peaks attributed to phase transition at 177 oC (KNH2SO3) and 182 oC (NaNH2SO3). Haussühl and Haussühl8 also detected phase transformation in CsNH2SO3.
The thermal decomposition of the compounds occurs in two distinct steps. The first step begins with an exothermic (386 oC) process followed by another endotherm (439 oC) at both atmospheres. This stage leads to the formation of an intermediate, stable over a wide temperature range: 450 oC to 800 oC (synthetic air) and 443 oC and 820 oC (N2). This intermediate is probably MnSO4 (Calc. = 47.31 %, TG = 47.34 %), that begins to decompose with an endothermic event (850 oC) to produce the oxide. In the temperature range in which the experiments were performed (30 oC → 900 oC) the formation of the residual oxide could not be observed.
The dehydration process of the cobalt (II) amidosulfonate occurs in a single step, with simultaneous elimination of three water molecules between 85 and 220 oC and loss of mass of 16.6 %. In this stage two endothermic peak are observed around 112 oC and 157 oC (synthetic air) and 111 oC and 164 oC (N2). After the anhydrous formation, an exothermic peak is observed around 210 oC, which may be associated with a crystallization process. The decomposition of the ligand occurs in two distinct stages: between 245 oC and 450 oC (synthetic air) and between 258 oC and 442 oC (N2), both with formation of the CoSO4 intermediate. In this step two endothermic DTA peaks are observed: 392 oC and 426 oC (synthetic air) and 400 oC and 433 oC (N2). The CoSO4 intermediate (Calc. = 50.80 %, TG = 51.80 %) remains stable over a wide temperature range: between 442 oC and 720 oC (synthetic air) and between 450 oC and 716 oC (N2). The formation of the residue occurs at 861 oC, with mass loss of the order of 26 %, compatible with the formation of CoO, in both atmospheres.
The dehydration of the nickel (II) amidosulfonate occurs in a two overlapping steps, with elimination of two water molecules between 90 and 192 oC (synthetic air) between 100 oC and 206 oC (N2) with mass loss of order of 13.5 %. At this stage, endothermic peaks are observed at 134 oC and 164 oC (synthetic air) and 132 oC (N2). After the anhydrous formation, an intense exothermic peak is observed at 203 oC (synthetic air) and 201 oC (N2) of low intensity, which may be associated with a crystallization process. The decomposition of the ligand occurs in two distinct stages: between 251 oC and 479 oC (synthetic air) and between 294 oC and 461 oC (N2), both with formation of the NiSO4 intermediate. In this stage endothermic DTA peaks are observed at: 304 oC, 411 oC and 462 oC (synthetic air) and 324 oC, 395 oC and 450 oC (N2). The NiSO4 intermediate (Calc. = 53.94 %, TG = 53.30 %) remains stable over a wide temperature range: between 474 oC and 720 oC (synthetic air) and between 459 oC and 716 oC (N2). The formation of the residue occurs at 831 oC (synthetic air and N2) with loss mass in the order of 26 %, compatible with the formation of NiO, in both atmospheres.
The dehydration of the copper (II) amidosulfonate occurs in a two overlapping steps, eliminating one water molecule between 73 oC and 199 oC (synthetic air) and between 65 oC and 203 oC (N2) with mass loss of 6.9 % in both atmospheres. At this stage, two endothermic peaks were observed at 89.6 oC and 196 oC in both atmospheres. After the anhydrous formation, an exothermic peak around 211 oC (synthetic air and N2) of low intensity is observed, which may be associated with a crystallization process. The decomposition of the ligand occurs in two distinct stages: between 200 oC and 450 oC (synthetic air) and between 206 oC and 440 oC (N2), both with formation of the CuSO4 intermediate (Calc. = 58.31 %, TG = 58.13 %). In this stage endothermic DTA peaks are observed: 343 oC, 420 oC and 436 oC (synthetic air) and 345 oC, 412 oC and 426 oC (N2). The CuSO4 intermediate remains stable over a wide temperature range: between 444 oC and 694 oC (synthetic air) and between 440 oC and 618 oC (N2). In this stage endothermic peaks are observed at 741 oC and 799 oC (synthetic air) and 718 oC and 773 oC (N2). The formation of the residue supposed CuO occurs at 810 oC (synthetic air) and 780 oC (N2). Under N2 atmosphere a new stage of mass loss appears, which begins at 840 oC and probably ends at temperatures above 900 oC. The DTA profile of the beginning of this stage has endothermic characteristics, suggesting a Cu2+→ Cu+ reduction process.
Dehydration Zn(NH2SO3)2.3H2O occurs two overlapping steps, between 64 °C and 195 °C (synthetic air and N2), equivalent to the consecutive release of one and two water molecules, respectively, with losses of the order of 17 %, Endothermic peaks are observed at 97 oC and 163 oC (synthetic air and N2). After formation of the anhydrous compounds, an exothermic peak was observed around 202 oC (synthetic air and N2). The anhydrous compound remains stable between 190 °C and 295 °C (synthetic air) and 196 °C and 322 °C (N2). The decomposition of the ligand in synthetic air starts at 304 oC, with endothermic peaks at 364 oC and 457 oC (synthetic air) and 364 oC and 465 oC (N2). This stage leads to the formation of intermediate ZnSO4 (Calc. = 51.80 %, TG = 52.40 %), which remains stable over a wide temperature range of 467 oC to 688 oC (synthetic air) and 471 oC to 684 oC (N2). In a synthetic air atmosphere, the decomposition to ZnO occurs from 690 oC and ends at 913 oC, presenting endothermic peaks at 804 oC and 900 oC. In nitrogen atmosphere, residual oxide formation is not completed until 920 oC and endothermic peaks are observed at 744 oC, 789 oC and 912 oC.
The main absorptions in the infrared: vO-H (3600 - 2700 cm-1) in the salts; vN-H (3400-3300 cm-1) in amidosulfonic acid; vsS-O (1260-1140 cm-1) and vasS-O (1040-1020 cm-1) emphasize the differences between the spectra of the salts and of the amidosulfonic acid, evidence the bond to the metal suggesting that the coordination occurs by the sulphonic grouping.
The X-ray diffractograms indicate that the compounds were obtained with a certain crystallinity degree, showing no evidence of isomorphism. The compounds showed relatively low intensity reflections.
The thermoanalytical results (TG/DTA) allowed to establish the stoichiometry of the compounds as: ML2.xH2O, where M represents the metallic ions Mn2+, Co2+, Ni2+, Cu2+ and Zn2+; L represents the anion NH2SO3-; x represents the number of water molecules, where x = 4 for Mn2+, x = 3 for Co2+; and Zn2+, x = 2 for Ni2+ and x = 1 for Cu2+. No significant differences were observed between the analysis carried out in synthetic air or nitrogen atmosphere, only the thermal decomposition of the ligand in synthetic air atmosphere occur at slightly lower temperatures that in a nitrogen atmosphere. For all compounds, the MSO4 stable intermediate was observed, which later decomposes to the respective oxide, that is: Mn3O4, CoO, NiO, CuO and ZnO. In some samples the residual oxide is produced at temperatures above 950 oC.
This research was supported by resources supplied by the Faculdade de Engenharia de Guaratinguetá (UNESP). The authors thank Prof. Dr. Edson Cocchieri Botelho (DMT-FEG-UNESP) for TG–DTA measurements, Prof. Dr. Sergio Francisco dos Santos (DMT-FEG-UNESP) for X-ray diffractometry, Prof. Dr. Konstantin Georgiev Kostov (DFI-FEG-UNESP) for FTIR measurements.
jose-marques.luiz@unesp.br
Elemental analysis of the solid compounds.
Figure 1.
Vibrational spectra in the infrared region of amidosulfonic acid and metal amidosulfonates.
Figure 2.
X-ray diffraction pattern of the metal amidosulfonates.
Figure 3.
TG and DTA curves of the obtained compounds, in a synthetic air atmosphere. Sample mass: Mn = 9.680 mg, Co = 2.980 mg, Ni = 10.194 mg, Cu = 10.314 mg and Zn = 10.064 mg.
Figure 4.
TG and DTA curves of the obtained compounds, in a nitrogen atmosphere. Sample mass: Mn = 10.383 mg, Co = 3,794 mg, Ni = 2,984 mg, Cu = 10.414 mg and Zn = 10.193 mg.
Results extracted from the TG curves.
Results extracted from the DTA curves.
